1. Field of the Invention
The present invention relates to a process cartridge and an image forming apparatus employing the same, and more particularly, to a process cartridge in which various imaging components including a photoconductor and a developer applicator are integrated into a single unit for detachable attachment to an image forming system, and an electrophotographic image forming apparatus, such as a photocopier, printer, facsimile, etc., employing such a process cartridge.
2. Discussion of the Background
Electrophotographic process cartridges are employed in many image forming systems, such as photocopiers, facsimiles, printers, etc., in which various imaging components are assembled into a single replaceable unit detachably attachable to an image forming apparatus. A typical architecture for a process cartridge includes a photoconductor section accommodating a drum-shaped photoconductor and a developer section accommodating developer with a developer applicator. When assembled and installed, the photoconductor and the developer roller define a development gap or zone therebetween, wherein the developer passes from one surface to another to develop an electrostatic latent image on the photoconductor into visible form.
As inconsistencies in the development process greatly affect final print quality of the image forming system, particularly in terms of toner density of printed images, maintaining a consistent gap between surfaces of the photoconductor and the developer applicator is important.
To provide such an efficient process cartridge, one conventional method proposes an architecture in which a photoconductor unit accommodating a photoconductive drum and a development unit accommodating a developer roller are assembled into a single unit with a pair of positioning members. The pair of positioning members, each screwed onto a side wall of the photoconductor unit, hold ends of the photoconductive drum and the developer roller on opposing sides of the process cartridge.
According to this method, the positioning members disposed on the ends of the photoconductive drum and the developer roller can create and maintain a proper development gap without damaging the photoconductive surface, in contrast to a configuration where a spring-loaded spacer is held against the photoconductive surface to provide spacing between the photoconductor and the developer applicator.
One drawback of this method, however, is that the positioning members attached solely to the photoconductor unit do not maintain the developer unit in position, and the development unit is provided with no support that firmly holds it along the length of the process cartridge. When the process cartridge is installed and operated, the unsteady development unit readily wobbles from side to side upon rotation of the developer roller, resulting in degraded development performance and toner leaking out of the wobbling unit to contaminate the interior of the image forming apparatus.
To address this problem, one possible approach is to fasten the positioning members to both the photoconductor unit and the development unit. However, this approach is not successful where the photoconductor and development units have variations in length (e.g., due to manufacturing variations) relative to their specified design lengths. Even if falling within manufacturing tolerances, such dimensional variations result in irregular side walls onto which the positioning members are fastened, causing displacement and deformation of the positioning members from their intended position and shape. Naturally, the positioning members, once displaced and/or deformed, cannot properly position the photoconductor drum and the developer applicator, resulting in an inconsistent development gap and concomitant variations in density of developed toner images.
Thus, what is needed is a stable and efficient architecture for a process cartridge which can hold a photoconductor and a developer applicator in proper operational position without damaging the photoconductive surface and irrespective of dimensional variations in constituent units of the process cartridge.